The present invention relates to new bridged bis(tetrahydro-indenyl)metallocenes, to the corresponding ligands and to catalysts for the polymerization of olefins containing them.
Stereorigid chiral metallocene compounds possessing two bridged cyclopentadienyl groups condensed to a C5-C7 ring are well known in the state of the art and are mainly used as catalytic components in olefin polymerization processes; in particular, metallocene compounds possessing two bridged indenyl or 4,5,6,7-tetrahydro-indenyl groups are widely used in the preparation of stereoregular polyolefins.
The numbering of the substituents on the indenyl group, to which reference is made in the present application, in accordance with the IUPAC nomenclature, is the following: 
In the bridged indenyl and tetrahydro-indenyl metallocene compounds known in the state of the art, the indenyl groups are linked together by divalent radicals generally linked to the 1 position of said indenyl groups, and therefore, the common indenyl metallocenes are 1-indenyl compounds.
For example, the European patent application EP 0 485 823 describes a class of bridged bis(1-indenyl)metallocenes, wherein the indenyl groups have a substituent other than hydrogen in the 2 position and are bridged in the 1 position by means of a bridge containing 1 or more carbon atoms (e.g. an ethylene or isopropylidene group) or containing heteroatoms (e.g. a dimethyl-silyl or a diphenyl-silyl group).
European patent application EP 0 485 821 describes a class of bridged bis(4,5,6,7-tetrahydro-inden-1-yl)metallocenes, bearing a substituent in the 2 position and bridged in the 1 position by means of an ethylene, isopropylidene, dimethyl-silyl or diphenyl-silyl group.
The European patent application EP 0 372 414 describes a very broad class of bridged or unbridged metallocenes; among the many metallocenes exemplified, two specific bis-indenyl metallocene compounds are reported, wherein the ethylene group bridging the indenyl groups is linked to the 1 position of one indenyl group and to the 2 position of the other indenyl group (formulae II-1 and II-2, on page 5 of said application). No tetrahydro-indenyl derivatives are mentioned.
The International patent application WO 94/11406 describes a very broad class of metallocene compounds of formula Rxe2x80x2Indxe2x80x94Mxe2x80x94(Cp)Qk, wherein: Ind is an indenyl group; Rxe2x80x2 is a substituent, other than hydrogen, linked in the 2 position of said indenyl group; Cp is a cyclopentadienyl group; M is a transition metal belonging to group 3, 4, 5 or 6 of the Periodic Table of Elements; and Q is a sigma-ligand of the metal M, k being an integer linked to the valence of M. Among the huge plethora of embodiments envisaged in the reported general formula, Rxe2x80x2 can form a bridge between the 2 position of the Ind group and the Cp group of the above formula. Even in this document, there is no reference to tetrahydro-indenyl derivatives. Moreover, the bis-indenyl zirconocenes tested in the working examples shows very poor activities in ethylene (co)polymerization, leading to products with unsatisfactory molecular weights.
The Applicant has now unexpectedly found a new class of metallocenes, particularly active as catalyst components for the polymerization of olefins; said metallocenes are characterized by the presence of two 4,5,6,7-tetrahydro-indenyl groups linked in the 2 position by means of a divalent bridging group. Therefore, an object of the present invention is a bridged bis(tetrahydro-indenyl)metallocene of formula (I): 
wherein:
M is a transition metal belonging to group 3, 4, 5, 6 or to the lanthanide or actinide groups of the Periodic Table of the Elements (new IUPAC notation);
the substituents X, the same or different from each other, are monoanionic sigma ligands selected from the group consisting of hydrogen, halogen, xe2x80x94R, xe2x80x94OR, xe2x80x94OSO2CF3, xe2x80x94OCOR, xe2x80x94SR, xe2x80x94NR2 and xe2x80x94PR2 groups, wherein the R substituents are linear or branched, saturated or unsaturated, C1-C10 alkyl, C6-C20 cycloalkyl, C6-C10 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table of the Elements (new IUPAC notation), such as B, N, P, Al, Si, Ge, O, S and F atoms, and two R substituents may form a 5-7-membered ring; preferably, the substituents X are the same;
(ZR1i)j is a divalent group bridging the two tetrahydro-indenyl residues, Z being selected from the group consisting of C, Si, Ge, N and P; the substituents R1, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table of the Elements (new IUPAC notation), such as B, N, P, Al, Si, Ge, O, S and F atoms;
the substituents R2 and R3, the same or different from each other, are selected from the group consisting of halogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table of the Elements (new IUPAC notation; such as B, N, P, Al, Si, Ge, O, S and F atoms), xe2x80x94OR, xe2x80x94SR, xe2x80x94NR2, N-pyrrolyl, N-indolyl, xe2x80x94PR2, xe2x80x94BR2 and xe2x80x94SiR3 groups, wherein the R substituents have the meaning reported above; or two adjacent R3 substituents form a ring having from 4 to 8 carbon atoms;
p is an integer ranging from 0 to 3, being equal to the oxidation state of the metal M minus 2;
i is 1 or 2; j is an integer ranging from 1 to 4; m is an integer ranging from 0 to 2; n is an integer ranging from 0 to 8.
Another object of the present invention is a catalyst for the polymerization of olefins comprising the product obtainable by contacting:
(A) one or more bridged bis(tetrahydro-indenyl)metallocene of formula (I), as described above; and
(B) a suitable activating cocatalyst.
Furthermore, the present invention provides a process for the polymerization of olefins comprising the polymerization reaction of one or more olefinic monomers in the presence of a catalyst as described above.
It is another object of the present invention a ligand of formula (II): 
or a double bond isomer thereof, wherein the double bonds of the cyclopentadienyl rings can be in any of the allowed positions, Z, R1, R2, R3, i, j, m and n having the meaning reported above, with the proviso that, when m is 0, then n is different from 0.